Fresh water supplies are under threat globally. Reverse osmosis, nanofiltration, and engineered osmosis (i.e. direct osmotic concentration and forward osmosis) technologies will aid in lowering the cost of water purification. In addition, pressure retarded osmosis, which is also an engineered osmosis technology, will be used to generate electricity. Desalination, brackish water treatment, scale control, and wastewater recovery are all applications of such technologies, growing in the 8%-15% per year range. Such technologies have different opportunities than traditional reverse osmosis and nanofiltration systems for developing efficiencies and cost-savings. With reverse osmosis, separation is driven by hydraulic pressure. This high pressure leads to high costs of operation because of large energy demands. With engineered osmosis technologies, separation is driven by osmotic pressure/concentration gradients. These flows occur spontaneously by osmosis.
Thin film composite (TFC) membranes have been in use for nanofiltration and reverse osmosis for many years. Such membranes are a composite of a selective, e.g., ion rejecting, membrane layer and a support layer. The development of these membranes has generally focused on the optimization of the selective membrane layer, which is thin, fragile, and highly permselective. Optimization of such membranes includes improving characteristics such as permeate production rates with lower energy input and imparting fouling resistance (see. U.S. Pat. No. 7,490,725 entitled “Reverse Osmosis Membrane and Process” to Pinnau).
Currently-used technologies can be inefficient and costly. Improvement of flux while maintaining ion rejection capacity is one way to develop efficiencies. Reducing the cost of manufacture of devices is a way to realize cost-savings.
There is a need to improve the support layers as a way to improve overall TFC membrane performance in the field of separation by ion rejecting membranes. This is particularly true when using membranes in nontraditional modes such as direct osmotic concentration (DOC), forward osmosis (FO), or pressure retarded osmosis (PRO).